1. Field of the Invention
The present invention relates to an apparatus and a method for opening and closing a lid of a closed container that is used to transport silicon wafers or the like between semiconductor processing apparatuses in a semiconductor manufacturing process etc. More specifically, the closed container is a container in which silicon wafers are stored and that is used to transport the wafers between the semiconductor processing apparatuses, and the present invention relates to an apparatus that opens and closes the lid of the container, a gas replacement apparatus that replaces the gas in the interior of the container, and what is called a FIMS (Front-Opening Interface Mechanical Standard) system or a load port apparatus that detaches the lid from the container to take out silicon wafers from the container and to allow transfer of the wafers into/out of the container.
2. Related Background Art
Previously, the semiconductor manufacturing process had been performed in what is called a clean room that is constructed by establishing a high degree of cleanliness in the room in which semiconductor wafers are handled. In recent years, however, in view of an increase in the wafer size and with a view to reduce cost incurred in maintenance of the clean room, use has been made of a method of keeping clean only the interior of a processing apparatus, a pod (i.e. a closable container for storing wafers) and a mini environment through which substrates or wafers are transferred between the pod and the processing apparatus.
The pod is a closed container composed of a substantially cubical main body having shelves provided therein that can hold a plurality of wafers in a parallel and separated state and an opening provided on one of the sides or external walls thereof through which wafers can be brought into/out of it, and a lid for closing the opening. Those pods which have an opening provided not on the bottom but on one lateral side thereof (i.e. the front side to be opposed to the aforementioned mini environment) are collectively called FOUPs (Front-Opening Unified Pods). The present invention mainly pertains to technologies that use the FOUP.
When wafers are stored in the pod, the interior of the pod is filled with so-called clean air from which contaminants such as dust have been excluded as much as possible to prevent contaminants such as dust from attaching to the wafers while the wafers are stored. In recent years, with decreases in the size of semiconductor devices and with enhancements of their performance, oxidization of the surface of the wafer or the surface of layers formed on the wafer by oxidizing atmosphere during wafer storage has become a problem. In view of this, it has been considered desirable that the interior space of the pod be filled with clean inert gas such as nitrogen gas. It has been considered more desirable that the interior space of the pod be filled with inert gas that is kept at a pressure higher than the pressure in the environment outside the pod.
To fill the interior space of the pod with inert gas, a load port apparatus (that is, an apparatus adapted to open/close the door of a pod to enable transfer of wafers into/out of the interior of the pod) like that disclosed in Japanese Patent Application Laid-Open No. 2004-235516 is typically used, and the lid is closed while inert gas is being supplied to the interior of the pod after all of the predetermined wafers have been inserted into the interior to achieve a desired enclosure condition. However, it is well known that the pressure in the interior of the pod in which the wafers are enclosed decreases with time, and the enclosure condition is degraded from a preferred condition with time. In view of this, a gas purge system as disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-005193 may be used to purge the interior of the pod again using fresh, clean inert gas at an appropriate timing. In the system disclosed in Japanese Patent Application Laid-Open No. 2006-005193, supply of the inert gas into the interior of the pod and discharge of the gas that has been enclosed in the interior are performed at the same time using an inert gas supply port and an exhaust port provided on the bottom of the pod to achieve gas purging.
In another method disclosed in Japanese Patent Application 2003-168727, the pod is kept in the interior of a closable chamber, and the inert gas in the interior of the pod is replace by fresh, clean gas by sequential operations of opening the lid of the pod in the chamber, reducing the pressure in the interior of the chamber and the pod, and supplying inert gas into the chamber and the pod.
However, there is a possibility that the following problem is encountered or will be encountered in the future by the above described prior art methods when they are put into practice. Specifically, in the case of the method disclosed in Japanese Patent Application Laid-Open No. 2004-235516, it is difficult to achieve sealing of the above-mentioned so-called mini environment since a drive system for means for holding the lid of the pod is provided. Therefore, the degree of purity of the inert gas supplied into the interior of the pod is hard to be enhanced beyond a certain level. Furthermore, there are many driving elements in the mini environment, and dust generated from such elements will be stirred up by down-flow produced in the mini environment. Therefore, there is a possibility that such dust enters into the pod. To reduce the possibility of the entrance of dust into the pod, the flow rate of the down-flow may be increased. But use of this countermeasure leads to an unduly large increase in the amount of inert gas used, which will be a problem in terms of semiconductor manufacturing cost.
In the case of the method disclosed in Japanese Patent Application Laid-Open No. 2006-005193, the amount of inert gas used can be made minimum, and this method is considered to have an advantage in terms of cost over the method disclosed in Japanese Patent Application Laid-Open No. 2004-235516. In addition, this provides other advantages that the structure of the apparatus can be made simple, that the possibility of generation of dust by gas supply and the possibility of entrance of dust into the pod are low, and that the area required to install the apparatus can be made small. However, in practice, since the direction of flow of the supplied and discharged inert gas is perpendicular to the planes in which the wafers stored in the pod extend, the gas replacement efficiency is low in the regions between the wafers, and there is a possibility that the gas cannot be replaced effectively even if purging is performed over a significantly long period of time. Furthermore, this problem can be more serious with an increase in the wafer diameter in recent years.
In the case of the method disclosed in Japanese Patent Application Laid-Open No. 2003-168727, it is necessary to prepare a chamber that can house the entire pod and means for decreasing the pressure in the interior of the chamber to a certain level. Thus, this method is disadvantageous in that the structure of the apparatus is complex and the size thereof is large. Generally, pods are stored and transported in environments in which the degree of cleanness is much lower than those in the interior of the pods, in the interior of the chamber, and in the aforementioned mini environment. For this reason, on the outer surface of the pod are dust or impurity gases etc. that have attached thereto. Thus, when the pod is brought into the chamber, the environment in the chamber can be contaminated with the extraneous matters. The possibility of such contamination can be excluded by replacing the atmosphere around the pod with high purity gas before opening the lid of the pod. However, this necessarily requires time for the gas replacement operation, and there arises a problem of elongation of the processing time. This problem can be more serious with an increase in the pod size necessitated by an increase in the wafer diameter in recent years.